1. Field of the Invention
In the application to optical coherence tomography, there is a need to detect reflecting and scattering targets within a sensing volume to determine the spatial distribution of the targets. The use of low coherence laser sources allows detection of reflecting and scattering targets by scanning optical paths through the zero path difference condition under which fringes can be observed. In the application to polarization mode dispersion (PMD), the source has passed through a long singlemode fiber and has accumulated phase and amplitude changes due to birefringence effects in that fiber which manifest as polarized modes which can be analyzed by observation of the fringes generated in a scan.
2. Discussion of the Prior Art
There are many descriptions of fiber optic interferometers with optical path length modulation that give fringes. These devices are made in single mode (SM) standard fibers that exhibit random changes in polarization state due to environmental conditions and can be compensated to some extent by the use of polarization controllers. Interferometers made in polarization maintaining (PM) fiber are usually restricted to one axis of polarization and have polarization stability, although cross coupled components give rise to unwanted modulation effects. Where a PM fiber has both axes transmitting light, the interference in each axis will generally be different and must be separated to give a useful device.